Analyte detection devices and methods with hematocrit/volume correction and feedback control

ABSTRACT

Disclosed are devices, arrangements and methods for quantifying the concentration of an analyte present in bodily fluid, including: an assay pad having at least one chemical reagent capable of producing a detectable signal in the form of a reaction spot upon reaction with the analyte; a light source; a detector array; a processor; and a memory in communication with the processor, the memory comprising: (a) at least one value indicative of one or more of: (i) the level of hematocrit contained in the sample; (ii) the volume of the sample applied to the assay pad; or (iii) imperfections present in the reaction spot; and (b) at least one algorithm for calculating the concentration of the analyte contained in the sample.

The present application claims priority pursuant to 35 U.S.C. §119(e) toprovisional application Ser. No. 60/689,546 filed Jun. 13, 2005, theentire content of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is directed to techniques and devices fordetection of the presence and/or concentration of an analyte.

BACKGROUND OF THE INVENTION

In the following discussion certain articles and methods will bedescribed for background and introductory purposes. Nothing containedherein is to be construed as an “admission” of prior art. Applicantexpressly reserves the right to demonstrate, where appropriate, that thearticles and methods referenced herein do not constitute prior art underthe applicable statutory provisions.

According to the American Diabetes Association, diabetes is thefifth-deadliest disease in the United States and kills more than 213,000people a year, the total economic cost of diabetes in 2002 was estimatedat over $132 billion dollars, and the risk of developing type I juvenilediabetes is higher than virtually all other chronic childhood diseases.

A critical component in managing diabetes is frequent blood glucosemonitoring. Currently, a number of systems exist for self-monitoring bythe patient. One such system may be termed a photometric system ormethod. In such systems, the first step is to obtain the sample ofaqueous fluid containing an analyte to be assayed, usually whole bloodor fractions thereof. The sample of blood may be obtained by a fingerstick or other means.

The fluid sample is then contacted with an assay pad or membrane.Contact is generally achieved by moving the assay pad or membrane intocontact with the liquid sample on the surface of the patient's skin.Following application to the pad or membrane, the target analyte presentin the sample passes through the assay pad or membrane by capillary,wicking, gravity flow and/or diffusion mechanisms. Chemical reagentspresent in the pad or membrane react with the target analyte producing alight absorbing reaction product, or color change.

The assay pad or membrane is then inserted into a monitor where anoptical measurement is then made of this color change. In thoseembodiments where the optical measurement is a reflectance measurement,a surface of the assay pad or membrane is illuminated with a lightsource. Light is reflected from the surface of the assay pad or membraneas diffuse reflected light. This diffuse light is collected andmeasured, for example by the detector of a reflectancespectrophotometer. The amount of reflected light is then related to theamount of analyte in the sample; usually the amount of light reflectedoff the surface of the assay pad or membrane is an inverse function ofthe amount of analyte contained in the sample.

An algorithm is employed to determine analyte concentration contained inthe sample based on the information provided by the detector.Representative algorithms that may be employed where the analyte ofinterest is glucose and the fluid sample is whole blood are disclosed,for example, in U.S. Pat. Nos. 5,049,487; 5,059,394; 5,843,692 and5,968,760; the disclosures of which are incorporated herein byreference.

Glucose monitoring technology that relies on the photometric method ofquantifying the glucose concentration in whole blood may be subject toerrors associated with variations in hematocrit level, or concentrationof red blood cells within the blood sample. Various methods have beenemployed to ensure the accuracy and repeatability of measured glucoseconcentration using the photometric method across a typical range ofhematocrit levels. A normal hematocrit level is 42-54% for men and36-48% for women. Overall, the normal range is from 36-54%, but for avariety of reasons, those who regularly test their glucoseconcentrations may have hematocrit levels even lower (anemia) or higher(polycythemia) than these normal ranges. This presents a challenge forthe development of accurate glucose monitoring. This is because themeter is typically designed or calibrated assuming the sample willcontain a hematocrit level somewhere in the normal range. Diabetics andclinicians make critical medical decisions in the management of theirdisease based on the readings provided by these meters. Thus, it wouldbe advantageous to have a photometric quantification method that is moreaccurate across a broader range of hematocrit levels.

Additionally, glucose monitors typically require that the user supply asufficient quantity of whole blood for an accurate reading. This volumehas been around 10 microliters or more in the past, but with thedevelopment of newer quantification technologies, the minimum volume hasbeen brought to as low as 1 microliter for photometric meters. This hasreduced the burden on diabetics in their testing by reducing the depthof the lancing and the effort to milk a relatively large amount of bloodfrom their lancing site. Again, the calibration of the meter isdeveloped with the assumption that this minimum supply has beendelivered to the test strip. If the user has not supplied a sufficientamount, then the meter generally displays an error code and the usermust test again. Further, a user may supply more than the typical amountof blood to the test strip, which may lead to an inaccurate result ifthe calibration of the strip is volume sensitive. It would beadvantageous for a photometric meter to have the ability to evaluate andadjust its internal calibration by detecting the amount of fluidsupplied to the reagent strip, and applying an appropriate calibrationparameter specifically chosen for that volume.

The development of a fully integrated glucose meter system requiresincorporating the processes of skin lancing, transfer of blood to thereagent test strip, and quantification of whole blood glucose all in asingle device. Such systems may not require any user intervention at allduring the quantification process as long as sufficient sample volume isobtained. An automated catalyst, such as heat, vacuum, or pressure maybe utilized to obtain a sample of body fluid, or whole blood.

One such device relies on the application of a specific magnitude andduration of a partial vacuum to the skin in order to facilitate theacquisition of a minimum required sample volume. For some individuals,this pre-programmed amount or duration of vacuum may be appropriate. Forothers, this pre-programmed catalyst may produce either an insufficientor excessive amount of blood, as well as other undesired outcomes, suchas excessive bruising (for those with fragile capillary networks), anunnecessary delay in obtaining results (for fast bleeding individuals),as well as excessive residual blood left on the skin. Thus, it would beadvantageous if the sample quantification detector could also determinein real-time whether or not a sufficient sample volume has been obtainedfor an accurate reading, and provide this information as feedback tocontrol the magnitude and/or duration of a catalyst. This feedbackdriven control would be a significant advantage for integrated glucosemonitoring technology.

Photometric assay pads or membranes for analyte concentrationmeasurements typically produce a circular or linear spot when thechemical reagents contained therein react with a fluid containing aspecific analyte, such as glucose, within whole blood. An ideal spot maybe defined as one in which the color across the spot is uniform andindicative of the concentration of the analyte. A spot which is notideal may be manifest in one or more of the following ways:non-uniformity of the primary color (e.g., variations in the intensityof blue); presence of non-primary color, such as red, which may beassociated with the presence and/or lysis of blood cells, and the abovecolor variations may be distributed randomly or non-uniformly across thespot.

For a variety of reasons, the quality of a spot developed as a result ofan analyte reacting with the reagent membrane may not be ideal asdescribed above. Such reasons may include one or more of: flaws ormanufacturing variations in the membrane structure; variations in theconcentration of the reagent enzyme; mishandling of the membrane duringmanufacturing; and unintended chemical reactions between the fluidand/or analyte and the reagent structure and/or membrane chemistry (suchas another medical drug within the blood sample reacting with thereagent enzyme).

Most devices on the market cannot detect or correct for low qualityspots. Their sensors, typically one or more photodiodes, do not have theability to discretely analyze the flaws within a reagent spot. Thus,there exists a risk that these systems may not provide an accuratereading in circumstances of a non-ideal spot.

SUMMARY OF THE INVENTION

According to the present invention, the state of the art has beenadvanced through the provision of arrangements, devices and techniquessuch as those described further herein, for accurately, efficiently, andeconomically determining the presence and/or concentration of ananalyte. According to the present invention, the state of the art hasbeen advanced, especially, but not exclusively, within the context ofpersonal glucose monitoring devices and techniques. Additionally, oralternatively, according to the present invention arrangements, devicesand techniques are provided which may overcome one or more of theabovementioned shortcomings associated with conventional systems andmethods.

Devices and methods are contemplated that may employ a detectorcomprising an array of detector elements or pixels to detect colorchange or intensity of reflected light associated with a photometricchemical reaction between the analyte and reagent chemistry. Optionally,the detector elements comprise CMOS-based detector elements. Inparticular, the CMOS detector elements help correct for differences inhematocrit levels and/or volumes associated with samples under analysis.An additional aspect of the present invention provides for CMOS-baseddetector elements that can provide feedback control for a connecteddevice that performs automated whole blood sampling and detection of ananalyte. In yet another aspect of the present invention, feedback fromCMOS detection elements is used to compensate for non-ideal reactionspot characteristics.

According to one aspect, the present invention provides a device formonitoring the concentration of an analyte present in bodily fluid, thedevice comprising a detector, the detector comprising a detector elementor pixel, the element or pixel comprising a CMOS sensor, a CCD sensor, aphotodiode or an infrared sensor, including both near-field andmid-field infrared sensors. Other sensing systems also contemplatedwithin the scope of the present invention include infrared, ultravioletand fluorescent sensing systems and electrochemical sensing systems,including reagentless sensing approaches.

It is therefore to be understood that reference herein to the detectorarray of the present invention may include any suitable detectorelement(s). The present invention is thus not limited to embodiments ofthe invention including CMOS or CCD detector elements, photodiodes,infrared, fluorescent, ultraviolet or electrochemical detector elements.

It is to be understood that the detector array is not limited only tolinear arrays. Non-linear arrays, such as polar, or area arrays, arealso contemplated by the present invention.

It is to be understood that reference herein to first, second, third andfourth components (etc.) does not limit the present invention toembodiments where each of these components is physically separable fromone another. For example, a single physical element of the invention mayperform the features of more than one of the claimed first, second,third or fourth components. Conversely, a plurality of separate physicalelements working together may perform the claimed features of one of theclaimed first, second, third or fourth components. Similarly, referenceto first, second (etc.) method steps does not limit the invention toonly separate steps. According to the invention, a single method-stepmay satisfy multiple steps described herein. Conversely, a plurality ofmethod steps could, in combination, constitute a single method steprecited herein.

According to an aspect of the present invention, there are provideddevices, arrangements and methods for quantifying the concentration ofan analyte present in bodily fluid, comprising: an assay pad comprisingat least one chemical reagent capable of producing a detectable signalin the form of a reaction spot upon reaction with the analyte; a lightsource; a detector; a processor; and a memory in communication with theprocessor, the memory comprising: (a) at least one value indicative ofone or more of: (i) the level of hematocrit contained in the sample;(ii) the volume of the sample applied to the assay pad; or (iii)imperfections present in the reaction spot; and (b) at least onealgorithm for calculating the concentration of the analyte contained inthe sample.

According to a further aspect of the present invention, there areprovided devices, arrangements and methods for quantifying theconcentration of an analyte present in bodily fluid, comprising:providing an assay pad comprising at least one chemical reagent;introducing a sample onto the assay pad; producing a detectable signalin the form of a reaction spot upon reaction of the at least onechemical reagent with the analyte; generating a signal based on lightreflected off the assay pad; calculating at least one value indicativeto one or more of: (i) the level of hematocrit contained in the sample;(ii) the volume of the sample applied to the assay pad; or (iii)imperfections present in the reaction spot; and calculating theconcentration of analyte contained in the sample by factoring in the atleast one value.

According to the above, the device may comprise a glucose meterintegrating some or all of the above-described features. The integrateddevice may be configured to perform at least one such photometricanalysis before reloading disposable components thereof becomesnecessary. The integrated device may be handheld or wearable. Theintegrated device may be in the general form of a wristwatch.

According to the present invention, the detector elements may compriseCMOS-based detector elements. Moreover, the detector array may be in theform of a linear array of CMOS-based detector elements or pixels.

According to the present invention, an integrated device may includemeans for extracting a sample of bodily fluid and can comprise a skinpiercing member and the application of one or more of: (i) vacuum; (ii)positive pressure; and (iii) heat.

According to the present invention, as described above, the device mayfurther comprise a computer-readable medium, the medium comprising atleast one of an algorithm and a look-up table. According to the presentinvention, the device may further comprise a microprocessor controller.

The above-described invention may further comprise at least one of alight source, one or more lenses, one or more light transmissionelements (e.g. optical fibers), optical diffusers and optical filters.

In certain embodiments of the above-described invention, the assay padmay comprise at least one chemical reagent that produces a color changedefining a reaction spot upon reaction with the analyte.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiments are illustrated in the drawings in which likereference numerals refer to the like elements and in which:

FIG. 1 is a flow diagram of a mode of operation according to certainaspects of the present invention.

FIG. 2 is a schematic illustration of an arrangement formed according tothe principles of the present invention.

FIG. 3 is a schematic diagram of a portion of the arrangement of FIG. 2.

FIG. 4 is a perspective view of a device formed according to anembodiment of the present invention.

FIG. 5 is a partial cutaway view of FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary arrangements and methods for the detection and measurement ofthe presence and/or concentration of a target analyte, such as glucose,bilirubin, alcohol, controlled substances, toxins, hormones, proteins,etc., will now be described.

In broader aspects, the current invention provides the ability tocorrect for broad variations in sample hematocrit levels in themeasurement of an analyte, such as glucose, during the course of thetest. The invention takes advantage of an imaging array of detectors toperform this correction and does not require any additional hardware. Inother words, no other distinct sensors or detectors, other than theimaging array, are required to calculate the correction. The very sensorthat is used to quantify the analyte within the sample may also correctfor hematocrit. Strategic algorithms that process the data from theimaging array provide real-time or near real-time information about thesample hematocrit level. Thus, more accurate results, regardless of thehematocrit level of the user, may be obtained via correction based onthe hematocrit level of the sample.

The current invention may also use appropriate algorithms to permitreal-time sensing of the amount of sample volume delivered to an assaypad. With this information, appropriate calibration parameters may beselected corresponding to the actual delivered volume. To correct forsample volume, algorithms similar to those used for hematocritcorrection may be used, where volume is substituted for hematocrit and aunique formulation and corresponding constants are determined.

The present invention offers the flexibility to improve the accuracy ofmeasured glucose for a broad range of sample volumes that are typicallydelivered to the assay pad of the meter system. In addition, samplingcatalysts such as vacuum, heat, pressure, etc. may be implemented orprovided automatically by the device to help ensure sufficient samplevolume is collected and analyzed. The invention provides information tothe meter system to know when and how much of the catalyst issufficient. Since the invention can measure or estimate the volume ofthe sample delivered to the assay pad, it can also provide feedback tostart, maintain or terminate the catalysts, as well as increase ordecrease the magnitude of the catalyst, based on this measured volume.This offers the advantage of adapting the device function to the user'sreal-time skin physiology, minimizing the risks associated with thecatalysts (bruising, scarring, excessive bleeding), reducing the energyconsumed by the system, and reducing the chance of a wasted testoperation (and the associated user's time, battery supply, and cost oftest strip) by ensuring a minimum sample volume is obtained, as well asminimizing the overall time to get a result from the system.

According to additional broad aspects, the present invention can processdata received from the detector array to compensate for irregularitiesor imperfections present in a reaction spot in order to improve accuracyof the analyte concentration method. The present invention includesdevices, arrangements and methods that include any of the abovereferenced aspects individually, as well as combinations of some or allof these aspects.

The current invention may employ a linear CMOS imaging detector array.Contrary to other approaches that describe the use of 2-D CCD imagingdetector arrays, the linear CMOS array detects light across a single rowof optical detectors (pixels) whose output is proportional to the amountof light incident to the pixel. Linear detector arrays offer anadvantage over 2-D imaging systems in simplicity and efficiency inprocessing the image information as long as the expected location ofreagent chemistry reaction or reagent spot is known and the associatedlight, which may be supplied by an LED, is reflected from this area andis imaged appropriately by the CMOS array.

The CMOS detector array may have an overall size that is comparable tothe size of the assay pad and the expected range of spot sizes thatdevelop on the pad. According to one alternative, the detector can belarger than the size of the pad. This construction can allow widertolerances in the relative position of the assay pad and the detector,and provide for additional in-process error detection and recovery(e.g., detecting or correcting for assay pad motion).

In addition to light sources such as LED's, various optical componentssuch as lenses, diffusers, light pipes, etc. may be integrated into thesystem to optimize the image size and resolution. Such a system mayutilize a commercially available linear CMOS detector array such as part# TSL1401R or TSL1401CS; from TAOS, Plano, Tex. This detector has 128pixels across an array of ˜19 mm in length. Light reflected off of whitesurfaces, such as an unreacted reagent pad, and received by the CMOSdetector results in a signal from each pixel that is conditioned toproduce a near maximum response up to 5 volts. Darker surfaces, such asfrom a color change associated with a reagent spot, will produce lowervoltage response for each pixel depending on the reagent chemistry,light source, optical path, and ultimately, the concentration of theanalyte (e.g., glucose).

A number of different arrangements comprising a quantification member,such as an assay pad, a sensor or detector, and one or more additionalcomponents are contemplated by the present inventions. Additionalexemplary arrangements are described in U.S. application Ser. No.10/394,230, entitled ANALYTE CONCENTRATION DETECTION DEVICES ANDMETHODS, the entire content of which is incorporated by referenceherein.

When coupled with an assay pad containing a photometric reagent, thesensor detects the change in color of the pad, and the output isprocessed as a change in voltage relative to that of the originalreagent color. Typically, about 10-50% of the pixels across the arrayare sufficient to resolve a spot of color change, but this can depend ona variety of factors, including CMOS sensor design, sample volume size,reagent dynamics, and the optical path between the pad and sensor.

Since the arrangements and techniques of the present invention canperform the assay without all of the pixels in the sensor array being inoptical registry with the reagent spot, it is contemplated by thepresent invention to utilize these free pixels in one or more possibleways. For example, a second assay may be performed at a different areaof the same assay pad, or on separate assay pad, at a locationcorresponding to the aforementioned unused pixels. The unused pixels maybe used for calibration or as a control. For instance, a controlsolution having a known concentration of analyte may be introduced inthe area of the assay pad, or onto a separate pad, in the area of theunused pixels. The control solution reacts with the reagent and thesignal produced by pixels can be calibrated in accordance with the knownanalyte concentration. According to another alternative, a means forcalibrating the reagent for lot information may be provided in the areaof the unused pixels, thereby eliminating the need for the user to setreagent lot calibration codes. A similar arrangement and technique wouldbe to utilize a standard color in registry with the unused pixels thatproduces a known reflectance signal. Upon reading this known signal, thearrangement, via a microprocessor and associated software and electroniccomponents, can verify whether or not the device is functioningproperly.

According to certain embodiments, sensor data can be acquired with ananalog-to-digital capture device, such as a PC board, and processed as alinear dimension data array whose size corresponds to the number ofpixels in the imaging array, such as 128 or 256 pixels. This data arraywill change over time as the reaction between the analyte (glucose) andthe reagent enzymes develops, reaches saturation and begins to dry out.

According to one embodiment, the current invention incorporates analgorithm for processing the information in the data array over time todetect and correct for the hematocrit in the blood sample. The rate ofcolor change over time across the detector array, and thus rate ofchange in signal of the data array, is dependent upon the relativeamount of plasma in the sample. A relatively high plasma content in agiven sample size will cause the sample to react with the reagentchemistry faster and develop a change in color more quickly than arelatively smaller plasma content. Since hematocrit level is inverselyproportional to plasma content, the rate of color change can be scaledinversely to hematocrit level.

The relation between rate of color change and hematocrit level willdepend upon a variety of variables, including the volume of the sampledelivered to the assay pad as well as the inherent reagent chemistry,optical path, light source and detector array. Consequently, a uniquecorrelation calibration between color change rate as detected by theCMOS imager and blood hematocrit level can be empirically determined andprogrammed into a memory device as a lookup table, or calculation.

Exemplary, non-limiting algorithm formulations to accomplish the aboveinclude:

-   -   1. Hct α δA(x,t)/δt; where Hct=hematocrit, α implies        proportional to, δ/δt=is the partial derivative with respect to        time (a measure of rate of change), and A(x,t) is a measure of        the array signal strength in the sensor at position x at time t.    -   Proportionality may be linear and of the form        Hct=m(δA(x,t)/δt)+C; where m and C are constants determined        empirically. Hematocrit proportionality correction may also be        better represented by polynomial, exponential, power or other        functions.    -   2. Hematocrit α δA(x,t)/δx; where Hct and α are as defined        above, and δ/δx=is the partial derivative with respect to        position x.    -   Again, proportionality may be linear and of the form        Hct=m(δA(x,t)/δx)+C; where m and C are constants determined        empirically. Proportionality may also be non-linear and        represented by logarithmic, polynomial, exponential or other        equations.    -   3. Hematocrit α δA(x,t)/δx δt; where Hct and α are as defined        above, and δ/δx δt=is the partial derivative with respect to        position x and time t.    -   4. Hematocrit α δ²A(x,t)/δ²x δ²t; where Hct and α are as defined        above, and δ²/δ²x δ²t=is the second order partial derivative        with respect to position x and time t.

Pixel position x ranges from the lower to upper limits and in the caseof a 256 pixel array, would range from 1 to 256. For a variety ofreasons, the algorithm may be limited to the evaluation of specificpositions or ranges within the array, such as between x=x_lower andx=x_upper, where x_lower may be 40 and x_upper may be 80.

Time t as referred to in these algorithms can refer to the time elapsedbetween known events within the analyte quantification process. Forexample, t=0 may be defined at the point in which blood is firstpresented to the reagent membrane, or when the imaging array firstdetects a predetermined threshold change corresponding to the arrival ofthe analyte to the reagent membrane.

Array signal strength A(x,t) corresponds to a measure of the color ofthe reagent membrane. Typically, this signal is initially processed as avoltage or a current. Those skilled in the art of photometric reagentsignal process will appreciate that subsequent transformation of thisdata into a measure of normalized reflectance R and/or to absorption viathe well-known calculation of K/S may be represented by A(x,t). Forexample:

K/S(x,t)=(1−R)²/2R; where R=A(x,t)_(Reacted) /A(x,t)_(Unreacted), where

A(x,t)_(Unreacted) refers to the array signal corresponding to thereagent membrane prior to any reaction with the analyte, andA(x,t)_(Reacted) the array signal corresponding to the membrane as itreacts with the analyte at array position x at time t.

Those skilled in the art will appreciate that combinations of theseand/or other similar algorithms would mathematically capture therelation between hematocrit and the rate of change of spot developmentin the membrane. Furthermore, the skilled reader would appreciate thatthe proportionality constants (m and C) are dependent upon theconditions of the reagent membrane (material, chemistry, lighting), thehardware and software specifications, and the nature and method in whichthe analyte is delivered to the membrane.

Thus, the appropriate calibration factor relating reflected light toglucose concentration would then be chosen based on the hematocritlevel. When the consumer uses the device, the meter detects color changeand applies the correct calibration factor for the user's hematocritlevel to the calculation of glucose content made by an algorithm alsocontained in the same, or a different memory device.

As an example of the above, if the glucose calibration curve is of theform:

R=m×[Glucose Concentration]+b; where R=the as-measured reflected lightsignal, and m and b are empirically determined constants.

A corrected signal R_(c), could be derived from a look-up table ofcorrection factors, F_(h), as a function of hematocrit level:

R _(c) =F _(h) ×R

This corrected signal would then be substituted into the above equationto calculate the hematocrit-adjusted glucose concentration.

Processing the data generated by the change in color caused by thereaction between the analyte and reagent chemistry in conjunction withthe speed and capacity of today's microprocessors would not add to therequired time to process the sample, yet would substantially increasethe accuracy and reduce the variability for analyte concentrationmeasurements associated with different whole blood hematocrit levels.

Various alternatives and modifications to the above-described embodimentrelated to detector data analysis to determine hematocrit levels arepossible. For example, such alternatives and modifications include oneor more of: evaluating the rate of pixel signal changes with respect totime; evaluating the rate of pixel change with respect to time and withrespect to associated pixels that also are changing (i.e., spatial andtemporal rate of change); evaluating the rate of pixel change withrespect to time for an individual pixel; evaluating the rate of pixelchange with respect to time for multiple pixels; evaluating the rate ofpixel change with respect to time for the pixel that detects the largestchange in color when enzymatic reaction and color change is complete;evaluating the rate of pixel change with respect to time for the pixelthat detects the largest change in color during the ongoing enzymaticreaction; evaluating the rate of pixel change with respect to time forthe pixel that detects the largest change in color after a lapse of apredetermined amount of time before any enzymatic reaction has actuallyoccurred; and evaluating the resolved volume of the sample (as describedearlier) at a specific time for which a fixed, prescribed amount ofblood has been delivered to the reagent pad (since measured sample sizeis proportional to plasma volume, which is inversely proportional tohematocrit).

Using the aforementioned detector array, the invention also contemplatesnovel arrangements, devices and methods for quantifying, in real-time,the amount of sample delivered to an analyte quantification member, suchas an assay pad. This method takes advantage of the discrete dataprovided by individual detector elements or pixels. As a reaction spotbegins to develop in the assay pad, the system described earlier canresolve a particular dimension associated with the size of the spot,such as width. This invention does not require that the spot be of aparticular shape, such as round, square, or rectangular, as long as thedetector array is oriented to resolve at least one dimension of the spotthat is proportional to sample volume. Assuming the assay pad and themethod by which the blood is delivered to the pad has been optimized toreduce the variability in spot development, the spot size will beproportional to the volume of blood sample.

The imaging system can resolve the spot size by identifying how manypixels or detector elements have detected a color change. Although thecolor change associated with the chemical reaction between analyte andenzyme may not be completed or reached equilibrium, the quantificationof the number of pixels that have detected a predetermined thresholdchange in color will be proportional to the spot size. Thus, a real-timeassessment of the spot size and thus volume can be computed.

Accordingly, the effect on glucose concentration calculations associatedwith various sample volumes may be empirically determined, and a lookuptable, equation, or calculation incorporated in a memory device whichmay then be used to select an appropriate predetermined calibrationfactor to provide a more accurate reading of the analyte concentrationfor a particular sample volume. Thus, an appropriate calibration factorbased on the actual sample volume may be applied to an algorithm used tocalculate glucose concentration.

As an example of the above, if the glucose calibration curve is of theform:

R=m×[Glucose Concentration]+b; where R=the as-measured reflected lightsignal, and m and b are empirically determined constants. A correctedsignal R_(c), could be derived from a look-up table of correctionfactors, F_(v), as a function of sample volume:

R _(c) =F _(v) ×R

This corrected signal would then be substituted into the above equationto calculate the volume-adjusted glucose concentration.

Various alternatives and modifications to the above-described embodimentrelated to detector array data analysis to determine sample size arepossible, for example, such alternatives and modifications include oneor more of: computing the number of pixels that have detected a changein color above a prescribed constant threshold at a particular point intime during the enzymatic reaction; computing the number of pixels thathave detected a change in color above a prescribed constant threshold atmultiple points in time during the enzymatic reaction; computing thenumber of pixels that have detected a change in color above a prescribedconstant threshold at a time in which the enzymatic reaction iscomplete; computing the number of pixels that have detected a change incolor above a variable threshold across the array; using abovestrategies to correlate output to actual sample volume at reagent pad;and using above strategies to predict sample volume to be delivered toassay pad after a predetermined amount of time.

Using the aforementioned detector array to detect the volume of thesample, the volume information can be used as feedback information, andutilized in devices such as an integrated meter. The definition of anintegrated device or meter in this context includes one which includesthe functions of acquiring a sample of body fluid or blood from theskin, transporting the body fluid or blood from the skin to aquantification area or assay pad, and quantifying the analyte(e.g.—glucose) in the sample via a photometric method.

In this embodiment, a catalyst such as vacuum, heat, pressure, vibrationor similar action is preferably applied to the sampling site tofacilitate the acquisition of sufficient sample volume of blood.Catalysts such as these can be effective in expressing sufficientlylarge volumes of blood even from alternative body sites that are lessperfused than the fingertips. To ensure that the catalyst is appliedwith sufficient magnitude and duration, this invention provides aconstruction and method to control the catalyst such that it operatesfor exactly as long as necessary. By quantifying the sample volumedelivered to the reagent pad in real-time, the detector array andassociated on-board data processing within the integrated device canprovide a feedback signal via a digital microprocessor controller orsimilar device which indicates either to increase, decrease, or keepconstant the magnitude of the catalyst, as well as to either continue orstop the application of the catalyst. Those experienced in the art ofcontrolling such catalyst mechanisms will appreciate that the controlsignal may be either binary or analog and use this informationaccordingly to control a pump (for vacuum/pressure), a motor (forvibration), a heating element (for increasing skin temperature) orcombinations thereof.

One such exemplary mode of operation is illustrated in FIG. 1. Asillustrated therein, a suitable catalyst, such as a vacuum created by asuitable mechanism or pump is initiated. Shortly thereafter the signalsfrom the detector array are analyzed and the sample volume estimated.This volume is compared with a target sample volume. If the volume issufficient, the catalyst is turned off. If the volume is insufficient,the reading and calculating processes are repeated until such time asthe target sample volume is reached. Once the target sample volume isreached, the analyte concentration determination may continue.

Various alternatives and modifications to the above-described embodimentrelated to detector array data analysis to provide feedback arepossible. For example, such alternatives and modifications may includeone or more of: providing a feedback signal corresponding to actualsample volume received at the assay pad; providing a feedback signalcorresponding to predicted volume anticipated to be delivered to assaypad; providing an analog feedback signal that is proportional to thevolume received at the assay pad; providing a digital feedback signalthat indicates either sufficient or insufficient quantity of samplevolume received; providing feedback signal based on imaging of analternative location within the meter that is not necessarily thereagent pad, but can also be imaged by the detector array to detectwhether a specific threshold of blood will be delivered to the reagentpad; and providing feedback signal based on imaging of an alternativelocation outside of the meter (such as on the skin) that can also beimaged by the detector array to detect whether a specific threshold ofblood will be delivered to the assay pad.

The discrete nature of the detection elements or pixels also allows fordetection of flaws and to distinguish them from regions of the reactionspot that are developing an appropriate or more ideal photometricreaction, even if they are randomly distributed.

For example, a detector array is arranged to scan the reaction spot,optionally coupled with appropriate optical magnification. An ideal spotwill produce little or no variation in signal response across the array.In the case of a non-ideal spot, the response of the pixels will varyspatially and temporally. A quantification algorithm which has one ormore of the following features could correct and/or ignore the reactionspot flaw(s) and have the potential to provide a more accuratemeasurement of the analyte concentration: identification and inclusionof data only from pixels which correspond to the appropriate andexpected color (e.g., screen for data corresponding to various shades ofblue only); identification and exclusion of data from pixels which donot correspond to the appropriate and expected color (e.g., screen outdata corresponding to shades of red); inclusion/exclusion of pixelinformation which does not change at a rate with respect to timeexpected for the appropriate color (e.g., rate of change of blue is notthe same as that of non-blue pixels); and inclusion/exclusion of pixelinformation which does not change at a rate with respect to time after aspecific elapsed time or during a specific time window expected for theappropriate color (e.g., blue pixels change from time t1 to t2 by x %,whereas non-blue pixels do not change by x % between time t1 throught2).

Combinations of the above strategies or similar ones may allow thealgorithm to successfully correct for non-ideal spots. It may even bethe case that a relatively small percentage of the spot area actually isideal, yet if the detector array can image this area even 1 pixel couldbe sufficient to provide an accurate reading of the analyte.

FIGS. 2-3 are schematic illustrations of at least some of the aspects ofarrangements, devices and methods of the present invention. Asillustrated therein, an arrangement 10, such as an integrated device ormeter may include a detector array 20, which can be provided in the formof a linear array of individual detection elements 30. Each detectionelement 30 is capable of producing a signal. The detection elements 30may comprise one or more CMOS-based detection elements or pixels. Thelinear array 20 is generally in optical registry with an assay pad 40.The relative vertical position of the assay pad and detector array 20may, of course, differ from the illustrated embodiment. In addition, theassay pad 40 and the detector array 20 may have a geometry that differsfrom that of the illustrated embodiment. The detector array 20 may belarger than the assay pad 40.

The assay pad 40 preferably contains at least one reagent. A mechanismmay be provided to transport a sample of body fluid, such as blood, tothe assay pad 40. According to the illustrated embodiment, a hollowmember 60, such as a needle, having one end in fluid communication withthe assay pad may provide a mechanism for transport. As a sample of bodyfluid is applied to the assay pad 40, a reaction between the reagent andthe analyte of interest (e.g., glucose) results in a color change on asurface of the assay pad 40 forming a reaction spot 50 in opticalregistry with the array of detector elements 30. The detector array 20corresponds in location to the spot 50 produces a signal in response tothe color change that is indicative of the presence of the analyte ofinterest. The signal can be used to estimate the volume of the sampleapplied to the reagent pad, monitor the kinetics of the reaction betweenthe reagent and the analyte, and ascertain irregularities in thereaction spot 50, as described above. This information can then be usedto correct the output (e.g., concentration of analyte present in thesample) of the device to account for the hematocrit level, volume ofsample presented to the assay pad 40, and/or irregularities in thereaction spot 50. The above-described arrangement 10 of features may allbe contained or integrated within a single device or meter.Alternatively, one or a combination of any of the above-describedfeatures may be incorporated into such a device.

The detector array 20 forms part of an arrangement 70 present in thedevice 10 for carrying out the various operations described herein. Asbest illustrated in FIG. 3, the detector 20 may contain a plurality ofdetector elements in signal communication with a device 72 having timingand control logic. The timing and control logic may include internal aswell external control signals. These signals typically include clock andframe start signals. External timing and control signals may begenerated by a microprocessor/microcontroller or other externalcircuitry. The detector array 20 may have analog signal output.Alternatively, the detector 20 may have a digital data interface.

As illustrated, the detector may comprise an internal signal amplifier74. Alternatively, the signal amplifier 74 may be external, as indicatedby the amplifier 74 shown in broken line. According to anotheralternative, the amplifier 74 may be entirely omitted. According to yetanother alternative, both an internal and external amplifiers 74 may beprovided.

The signal from the detector 20 is outputted to an analog/digitalconverter 76 (where no digital data interface is provided by thedetector). The converter 76 is connected to a bus 78, along with amemory 80 and an input/output device 82. The memory 80 may comprise oneor more of RAM, ROM or EEPROM, as well as other conventional memorydevices. Whatever its form, the memory 80 preferably contains at leastone value indicative of hematocrit level, sample volume or reagent spotimperfections. In this regard the memory may contain one or more of thealgorithms and look-up tables described herein.

The converter 76, the bus 78, the memory 80 and input/output device 82may be components of a microprocessor/microcontroller 84. According toan alternative embodiment, the converter 76, memory 80 and input/outputdevice 82 are external to the microprocessor/microcontroller 84.

The input/output device 82 is in signal communication with variousoutput devices 86, 88, 90, 92, and can provide control signals thereto.These output devices may include a device providing a catalyst tofacilitate sample acquisition, as described herein. For example, thesedevices may include one or more of a vacuum pump, an actuation triggerdevice, a light source, a heat source, a vibration motor, orcombinations of any of the foregoing. Regardless of the form of thesedevices, they are configured and arranged such that they are in signalcommunication with input/output device 82 so as to be responsive to thecontrol signals. These control signals may be based on sample volumecalculations made with the assistance of the detector array, asdescribed herein.

An integrated device formed according to the principles of the presentinvention may have a number of suitable configurations. According tocertain embodiments the device is configured to perform testing byacquiring a sample of blood from the user, transfer the sample to ananalysis site, and determine the concentration of a target analytecontained in the sample. These operations are all performed with littleor no user input. For example, these operations may commenceautomatically according to a specified or predetermined schedule.Alternatively, these operations may commence at the command of the uservia, for example, pressing a start button on the device.

The device may include disposable and reusable portions. The disposableportion may include at least one skin piercing element/transport memberand analysis site (which may include an assay pad). The disposableportion may provide the capability to perform a single test. Aftertesting is complete, the disposable portion is discarded and replacedwith a new disposable portion before performing another test.Alternatively, the disposable portion includes a plurality of skinpiercing elements/transport members and analysis sites. Such disposableunits permit a plurality of tests to be performed before it is necessaryto discard and replace the disposable unit. The device may be eitherwearable or handheld, or both.

A non-limiting exemplary integrated device 100 is illustrated in FIGS.4-5. As illustrated therein the device 100 generally comprises afunctional portion 102, and an optional attachment means or band 104.Thus according to the present invention, the integrated device 100 maybe wearable. In addition, or alternatively, the integrated device may beoperable as a hand-held device. For example, according to theillustrated embodiment, the band 104 can be separated and/or otherwiseremoved from the user, and the device 100 stored in a suitable case orin the user's pocket. The band can then be grasped and used to hold thedevice against the skin to perform a testing operation.

The device 100 preferably includes at least one arrangement forperforming a measurement of the concentration of an analyte contained ina sample of blood. According to the illustrated embodiment, the device100 comprises at least one skin-piercing element, at least one actuationmember, such as a torsional spring element as described in furtherdetail herein, and at least one analysis site 110, which may contain anassay pad. The at least one arrangement may form part of a disposableportion or unit. According to one embodiment, the disposable unit allowsfor at least one measurement of the concentration of an analytecontained in a sample of blood prior to being discarded and replaced.According to a further embodiment, the disposable unit allows for aplurality of measurements of the concentration of an analyte containedin a sample of blood prior to being discarded and replaced.

According to certain alternative embodiments, the device mayadditionally contain one or more of the features disclosed in U.S. Pat.No. 6,540,975, U.S. Patent Application Publications 2003/0153900,2004/0191119, and published PCT Applications WO 04/085995 and WO04/0191693, the entire contents of which are incorporated herein byreference.

While this invention is satisfied by embodiments in many differentforms, as described in detail in connection with preferred embodimentsof the invention, it is understood that the present disclosure is to beconsidered as exemplary of the principles of the invention and is notintended to limit the invention to the specific embodiments illustratedand described herein. Numerous variations may be made by persons skilledin the art without departure from the spirit of the invention. Theabstract and the title are not to be construed as limiting the scope ofthe present invention, as their purpose is to enable the appropriateauthorities, as well as the general public, to quickly determine thegeneral nature of the invention. Unless the term “means” is expresslyused, none of the features or elements recited herein should beconstrued as means-plus-function limitations pursuant to 35 U.S.C. §112,¶6.

1-27. (canceled)
 28. An arrangement for measuring the concentration ofan analyte contained in a sample of body fluid, the arrangementcomprising: an assay pad comprising at least one chemical reagentcapable of producing a detectable signal in the form of a color changeat a reaction spot formed upon reaction with the analyte; a lightsource; a detector array; a processor; and a memory in communicationwith the processor, the memory comprising: (a) at least one valuederived from the color change at the reaction spot indicative of one ormore of: (i) the volume of the sample applied to the assay pad; and (ii)imperfections present in the reaction spot; and (b) at least onealgorithm for calculating the concentration of the analyte contained inthe sample using the at least one value.
 29. The arrangement of claim28, wherein the assay pad comprises only a single chemical reagent. 30.The arrangement of claim 28, wherein the detector array comprises aplurality of pixels, and wherein the at least one value derived from thecolor change at the reaction spot indicative of the volume of the sampleapplied to the assay pad is based on the number of pixels in thedetector array that have detected the color change.
 31. The arrangementof claim 28, wherein the at least one value derived from the colorchange at the reaction spot indicative of imperfections present in thereaction spot is based on deviations from an expected color or anexpected rate of color change.
 32. The arrangement of claim 28, whereinthe analyte comprises glucose and the body fluid comprises blood. 33.The arrangement of claim 28, wherein the detector array is a lineararray.
 34. The arrangement of claim 28, wherein the detector arraycomprises at least one of a linear array, a polar array, and an areaarray.
 35. The arrangement of claim 28, wherein the detector arraycomprises a plurality of detector elements, the detector elementscomprising CMOS, CCD, photodiode, infrared, fluorescent, ultraviolet, orelectrochemical elements.
 36. The arrangement of claim 28, furthercomprising at least one body fluid sampling catalyst device.
 37. Thearrangement of claim 36, wherein the at least one catalyst devicecomprises at least one of a vacuum pump, a vibration motor, and aheating element.
 38. The arrangement of claim 36, wherein the at leastone catalyst device is configured to be responsive to control signals,the control signals based on sample volume calculations.
 39. Thearrangement of claim 35, wherein at least a portion of the plurality ofdetector elements are not in optical registry with the reagent spot andare configured to analyze one or more of a control solution having aknown concentration of analyte introduced onto an area of the assay padthat is different from the area of the reagent spot, a standard colorproducing a known signal, and calibration information specific to thelot of the assay pad.
 40. The arrangement of claim 28, wherein thememory comprises at least one look-up table, and the at least one valueis stored in the at least one look-up table.
 41. The arrangement ofclaim 28, wherein the memory comprises a formula for deriving acorrected signal, the formula comprising:R _(c) =F _(x) ×R where R_(c) is the corrected signal, F_(x) is the atleast one value indicative of the volume of the sample, and where R ismeasured reflectance.
 42. The arrangement of claim 28, furthercomprising a needle having a first end configured to pierce the skin,and a second end in fluid communication with the assay pad.
 43. Ananalyte monitoring device comprising the arrangement of claim 28,wherein the arrangement comprises a plurality of assay pads and aplurality of needles, thereby enabling the performance of a plurality ofanalyte concentration measurements.
 44. The analyte monitoring device ofclaim 43, further comprising a band for attaching the device to the bodyof the user.
 45. An integrated meter comprising: at least one piercingelement; at least one actuation member; and the arrangement of claim 28.